The interaction of macrophages with an obligate intracellular microbe (Toxoplasma gondii) and a facultative intracellular microbe (Mycobacterium tuberculosis) will be studied. The intracellular events associated with phagocytosis of these microbes by macrophages from normal and immunized animals will be studied using phase contrast and electron microscopy, radioactive labelling techniques, and C14-l-glucose utilization and calculation of generation times. Primary and secondary lysosomes will be labelled with lysosomal markers, and the fusion of lysosomes with parasitized vacuoles will be examined. The effect of sensitized lymphocytes and lymphokines on the intracellular events in macrophages after phagocytosis of toxoplasmas or mycobacteria will also be investigated. It is expected that study of this lymphocyte macrophage model will add important dimension to our knowledge of intracellular parasitism and cellular immune responses.